The YBCO coated superconductor appears to have a promising future in such applications as power cables, magnets, electric motors, and current limiters, to name only a few. However, it is likely that such applications will require the A coated conductor to be exposed to time-varying magnetic fields or carry timevarying electrical currents. Such currents could be the common sinusoidal alternating current fields and/or direct currents with a xe2x80x9cripple.xe2x80x9d In these situations, energy losses will occur as the magnetic field associated with the current enters and leaves the superconductor. Losses like this are termed hysteresis losses. The particular details of the manner in which magnetic flux enters and moves within the superconductor can have a profound influence on the hysteresis losses. Unfortunately, hysteresis losses generate heat within the superconductor that increases the refrigeration required to maintain the superconductor in the superconducting state.
Hysteresis losses can have significant economic and technical impact on the application of superconductors to real world situations. They may make some applications uneconomic or even unviable because of the engineering problems they create.
Typically, the YBCO superconductor coated conductor is manufactured as a high aspect ratio ribbon, approximately 1 cm wide. With the YBCO superconductor itself only on the order of 1 xcexcm to 10 xcexcm thick, an aspect ratio of about 104 is produced. This very large aspect ratio dominates the mechanism by which magnetic flux and electric current distribute within the superconductor, and thereby the hysteresis losses. In particular, a high aspect ratio has been shown to cause very non-uniform distribution of the magnetic field within the conductor, with the local magnetic field being enhanced at the edges of the conductor ribbon. This is often referred to as xe2x80x9cstripxe2x80x9d geometry effects, which are considered to produce anomalously high alternating current hysteresis losses in the superconductor compared to what is expected, and has been measured, in lower aspect ratio superconductors, such as circular, often referred to as elliptical geometry.
It is to be understood that the higher loss is due to the geometry and not the superconducting material itself. The same YBCO material in the form of a circular cross section, for instance, would exhibit very different magnetic field distributions than when in a ribbon configuration, and the hysteresis losses would have very different dependence on applied field or transported current. The level of losses in the coated ribbon conductors has been demonstrated to be sufficiently high so as to limit severely their use in electrical power engineering applications. Some means of reducing these hysteresis losses in ribbon superconductors is therefore needed in order to enable the widespread use of this valuable material.
It is therefore an object of the present invention to reduce significantly reduce the hysteresis losses in superconductor coated conductors.
It is another object of the present invention,to provide superconducting conductors in a ribbon configuration for use in electrical power applications.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, a method of reducing hysteresis losses in superconductor coated ribbon having a critical current comprises the steps of establishing a transport electrical current greater than the critical current in the superconductor coated ribbon for a period of time sufficient to establish pinning of flux lines Within the superconductor coated ribbon.
In a further aspect of the present invention and in accordance with its objects and principles a method of reducing hysteresis losses in a superconductor coated ribbon having a face and a critical temperature comprises the steps of applying a magnetic field to the superconductor coated ribbon in a direction perpendicular to the face; and cooling the superconductor coated ribbon to a temperature below the critical temperature; whereby a magnetic flux distribution is established inside the superconductor coated ribbon.
In a yet further aspect of the present invention, and in accordance with its objects and principles, a method of reducing hysteresis losses in a superconductor coated ribbon having a face and a critical temperature comprises the steps of cooling the superconductor coated ribbon to a temperature lower than the critical temperature; and applying a magnetic field to the superconductor coated ribbon in a direction perpendicular to the face; whereby a magnetic flux distribution is established inside the superconductor coated ribbon.
In a still further aspect of the present invention, and in accordance with its objects and principles, a method of reducing hysteresis losses in a superconductor coated ribbon deposited onto a metallic substrate and having a critical temperature comprise the steps of applying a direct current magnetic field to the superconductor coated superconductor ribbon; and cooling the superconductor coated ribbon to a temperature below the critical temperature; whereby a magnetic field distribution is established inside the superconductor coated ribbon.
In a still further aspect of the present invention, and in accordance with its objects and principles, a method of reducing hysteresis losses in superconductor coated ribbon having a transition temperature comprises the steps of winding an electrical conductor around the superconductor coated ribbon; and passing a direct current through the electrical conductor; and cooling the superconductor coated ribbon to below the critical temperature; whereby a magnetic field distribution is established inside the superconductor coated ribbon.